Pre/Power Amplifiers

You could have knocked me down with a feather when, late last year, I received an e-mail from Adrian Walker, one half of the dynamic duo behind the original Deltec Precision Audio. I had used DPA’s 100S pre/power combination for the best part of a decade in my own system, and reviewed the inaugural product in HFN Oct ’87, but the company had dropped off our collective radar by the late 1990s. Rob Watts, the pioneering engineer behind the outfit, had moved on to other projects including a now longstanding relationship with Chord Electronics. Yes, Rob Watts ex- of DPA is the same Watts behind the WTA digital filter used in Chord’s Red Reference CD player.
   But I digress. Deltec, or at least one half of the original partnership, was now back with new versions of its fabulous Gore-Tex sheathed cables, a revised RF mains filter and most thrilling of all, a new preamp and mono power amp combination. This I had to hear.

THICK FILM HYBRID
   The aesthetics of the new DPA-CA1 preamp and 60W DPA-MA1 mono power amplifiers are clearly inspired by their earliest predecessors with simple but robust rotary controls and not a remote control in sight. The front panels are machined from alloy and topped-off with a high gloss blue/black automative finish while the folded alloy covers are linished and black-anodised. Twenty-two years on, this look will still polarise opinion!
   Both pre- and power amplifiers are built around a new thick-film hybrid op-amp, the DH-OA37, itself inspired by the DH-OA32 that debuted in Deltec’s earlier ’50S pre/power combo. The use of close-coupled surface-mount components allows for better control of the op-amp’s ‘RF environment’ than might be achieved with a full-sized PCB. Meticulous RF filtering is also a core feature of DPA’s power supplies, helping to rid the amplifiers of what it considers to be an insidious catalyst of distortion.

FEEDBACK REQUIRED
Another key feature of DPA’s earliest power amplifiers was the dual or double-pole negative feedback that allowed for a deep but uniform level of compensation right through to the highest treble frequencies. This latest DPA-MA1 applies its feedback in a more conventional form so distortion rises with frequency in the manner of most other amplifiers.
   Furthermore, the original DPA amps extended their feedback network out to the very tips of the speaker cable. Compensating for the cable was novel but not unique (the Trio Corporation of Japan – latterly Kenwood – had used this technique some years before) and also potentially hazardous. Short the speaker cable for an instant and the amp might attempt to dump a huge current into the link. Among other reasons, this could explain why so few DPA-50S and ’100S amps survive to this day and why the  DPA-MA1 extends its feedback to the 4mm speaker outlets and no further, like Deltec’s DPA-200S from 1993.
   As discretion is typically considered the better part of valour, I can accept this small compromise but I’m less sanguine about the lack of balanced inputs/outputs on either the CA1 or MA1. After all, at £6700 all-in and with a rated output of just 60W/8ohm these amplifiers are playing with the big boys of the high end league where XLRs are the norm, not the exception. It’s even more puzzling when you consider that the internal architecture of both products is at least pseudo-balanced.
   Other than this, the cool-running CA1/MA1 are simplicity itself to install, although you do have one important choice to make. Because the DPA-MA1 is a mono amp you can place it hard up against the speaker, rather than employ long leads, thereby deriving the maximum benefit from its uncommonly low output impedance. The DPA-CA1 is purpose-designed to drive long pre-to-power interconnects, for this reason.
   My media room is pre-wired with long interconnect (Townsend DCT) and speaker cable (QED XT400) to facilitate such comparisons and, in this instance, the ‘long distance’ pre/power installation won hands down.

RE-LIVING THE PAST
Anyone who has spent the best part of 25 years auditioning literally hundreds of different amplifiers, disc players and speakers will have developed a knack for establishing the broad capabilities of a product within a very short listening period. So it was not without some little frustration that after several hours of trawling through tried-and-tested high-resolution SACDs and Blu-ray media I was still staring down at a blank Word document on my notebook.
   There was more than a hint of the old ‘Deltec sound’ to commend them, the judicious RF filtering enabling you to pick out miniscule details from very dark and brooding silences. Perhaps I was trying too hard to like these new DPA amplifiers. After all, the original DPA-100S combination had given trusty service at the heart of my stereo system during countless sessions in the 80s and 90s, only being replaced by a multichannel solution in the last decade.
   But this CA1/MA1 combination did not deliver its music with the same transient precision, the same strength and solidity as its predecessor. I know: I recovered my ’100S out of storage, gently brought it to 240V and left to it simmer before performing level-matched comparisons. Ultimately this didn’t prove too helpful. After all, and despite conceptual similarities, the CA1/MA1 was a new amplifier, designed by a new engineer with different ideas, techniques and methods of implementation. The familiar case design and DPA logo was proving a psychological distraction, so I turned out the lights.

SOUND OF SILENCE
   One consistent feature of this new DPA pre/power lies its incredibly silent background. Not a whisper could be heard from my B&W’s tweeters until the music struck up and then what emerged was as sweet as the proverbial nut – delicate, feather-light percussion, crisply-defined and rich in harmonic colour.
   Re-mastered SACDs from The Police and Frankie... [A&M 493 698-2 and ZTT177SACD] provided repeated illustrations of this refinement, the percussive accompaniment to ‘Message in a Bottle’ and ‘War’ creating spotlights of soft illumination into a musical soundstage that readily wafted free of the speakers. But as the music built in intensity, the glimmer of this sweet treble was often overwhelmed by the busier, bustling sound of vocals, strings and drums. Without question, the music had energy and conviction but the see-through transparency enjoyed with simpler material was becoming overwhelmed. Listen to Billy Joel’s ‘...Always a Woman’ [Columbia SACD CS69384] and the warmth of his voice cosseted by the gentle insistence of the piano demonstrates the DPA combo at its luxurious best, a sound that has brilliance but never brightness.

HI-RES THRILLS
The vivid yet gentle thrill of strings from 2L’s audiophile recording of Mozart’s Violin Concertos (Marianne Thorsen/TrondheimSolistene on Blu-ray) was also faithfully resolved through these amplifiers, even if I was not tempted to wind up the volume to recover a greater sense of the church’s spaciousness and ambience. This is a fabulous recording from a DXD source (24-bit/352.8kHz) that lets you hear the resin-infused tension of the strings in startling detail. The Allego passage moved with an intonation that was almost vocal in character, the atmosphere of the event breathing from the DPAs with a pure, dare I say ‘organic’ energy and presence.
   In truth, it’s heavier-sounding discs that give the MA1 pause for its seemingly fickle bass either provides a slick but firm foundation for the performers or simply gets ahead of itself and rolls unceremoniously outward.

PROMISES, PROMISES
Contrary to the control promised by the amplifier’s uniquely low output impedance, Frankie’s powerful rendition of ‘Born to Run’ was pot-marked with surges of over-enthusiastic low frequencies. So too was the intro to Pink Floyd’s Dark Side of the Moon [EMI 7243 582136 2] where the bass would bloom quite unexpectedly. Perhaps speakers with less bass extension might be a smart idea. Or perhaps DPA’s undeniably innovative CA1/MA1 needs one final polish.

VERDICT
Aspects of the original DPA amplifiers are still in evidence here from the stylised casework, the thick-film hybrid op-amp, scrupulous attention to RF filtering and novel use of feedback. Similar ingredients, certainly, but stirred by new hands into amplifiers that offer a different flavour. The final brew is dark and smooth but often complicated in its resolution of the busiest details. The pheonix has risen, but it’s not quite on fire.

Originally published in the November 2009 issue